1. Field of the Invention:
The present invention relates to a process for an activated-sludge treatment of sewage or industrial waste water, and more particularly to one in which a novel fixing carrier for the activated sludge is employed to realize a high-efficiency activated-sludge treatment of the sewage or industrial waste water.
2. Description of the Prior Art:
For example, as for the sewage, the activated-sludge treatment thereof is generally conducted as follows:
The sewage accumulated in a sewage-treatment plant passes through a sand-sedimentation tank and a primary-sedimentation tank so that most of grit and coarse suspended matter is removed. After that, the sewage is allowed to flow into an aeration tank of an activated-sludge treatment process so that pollutants of the sewage are decomposed. Then, aeration tank effluent flows to a final sludge thickener (sludge-settling tank) in which the activated sludge is precipitated/separated, and the thickener effluent is subjected to a chlorination-treatment and the like and then discharged. On the other hand, a part of the activated sludge having been precipitated in the final sludge thickener is returned to the aeration tank as a return sludge, while the remaining part of such activated sludge is taken out and subjected to a methane-fermentation treatment, an incineration treatment and the like so as to be discarded.
Such activated-sludge treatment of sewage suffers from many problems. For example, the activated sludge produced in the treatment of the sewage is high in SVI (Sludge Volume Index), which leads to a difficulty in obtaining in the final sludge thickener a precipitated or settled sludge which is excellent in consolidation properties. In addition, the activated-sludge treatment has a defect in that when the treatment is conducted under a high-load condition or with a large load variation, or when thread like bacteria (hypomycetes) are developed in the activated sludge, the activated sludge suffers from bulking which leads to a poor settlement of the activated sludge. Consequently, it is hard for a conventional activated-sludge treatment of sewage to keep the activated sludge of the aeration tank in high concentration, which leads to limits of improvement of the treatment in its efficiency or in reduction of the time needed for conducting the treatment and compactness of the installations for conducting the treatment. Further, occurrence of bulking causes the activated sludge, which flows out of a sludge-settling tank, to lead to deterioration of the quality of the activated sludge effluent. As a result, under the conventional activated-sludge treatment, sewage disposal plants must be constructed in large-scale areas. In addition, it is hard to simplify the process of the treatment and it is also hard it to attain compactness of the installations of the treatment. Consequently, a considerable cost is needed for constructing a sewage disposal plant.
As a measure for resolving such inherent problems in the disposal of sewage, there is required a high-efficiency activated-sludge treatment technique to be developed.
As for the sewage or industrial waste water, hithereto, as an activated-sludge treatment process of high efficiency, there is provided a process for maintaining the activated sludge of the aeration tank in a high concentrations condition, which process is classified into a fluidized-bed system and a fixed bed system.
In the fluidized-bed system of the process, an example of which is disclosed in Japanese Laid-Open Patent Publication No. 61-136491, fine particles of grit such as diatomaceous earth, sand, ceramics and the like, or particles of activated carbon, or particles of organic high-molecular compounds are added to the aeration tank so as to be fluidized by aeration to cause the activated sludge to adhere to these particles, so that the activated sludge is improved in its settleability and maintained in a high concentration in the aeration tank.
In the fixed-bed system of such process, an example of which is disclosed in Japanese Laid-Open Patent Publication No. 61-136490, ceramic articles serve as the fixing carriers for the activated sludge. In this system, any honeycomb tube made of organic high-molecular compounds, multi-layer boards, ceramic articles and the like is immersed in the aeration tank to cause the activated sludge to adhere thereto, so that the activated sludge is fixed to the tube.
However, these conventional processes suffer from many problems. First, in a fluidized-bed system of the process employing fine inorganic particles, since the affinity of the activated sludge with such fine inorganic particles is not sufficient, it is required that the activated sludge adhere to such fine particles for an extended period of time in a stable manner. In addition, there is still not sufficiently established a process for treating the activated sludge having adhered to such carrier, an excess amount of sludge. Further, in the case of powdered activated carbon and particles of organic high-molecular compounds being employed in the fluidized-bed system of the process, since the affinity of the activated sludge with these particles is large, it is possible for the activated sludge to adhere to such particles in a stable manner. However, in the case wherein the excess sludge, having been treated through such process, is further treated through a methane-fermentation treatment, it is impossible to reutilized these particles after completion of methane fermentation of the excess sludge, since techniques for reutilizing such particles are still not sufficiently established. Further, in case that the disposal of the excess sludge is conducted through incineration, these carrier particles cause the cost of the sewage treatment to increase relative to the case wherein the inorganic-carrier particles are employed.
On the other hand, in a fixed-bed system in which a honeycomb tube of organic high-molecular compounds is used, the laminated boards and the like serve as fixed-bed type carriers for the activated sludge, since the affinity of the activated sludge with these carriers is large, the activated sludge having been proliferated adheres to these carrier, so that it is apt to cause them to clog. Consequently, in this case, it is necessary for the carriers to be frequently taken out of the aeration tank and cleaned through rinsing and the like so as to be regenerated. However, since the fixed bed is generally complex in construction while the affinity of the activated sludge with the carriers is large, it isnot possible, by a simple rinsing, to regenerate the carriers. Consequently, in order to regenerate such carriers, it is required a cumbersome treatment of the carriers. Further, in a process in which the conventional ceramic articles serve as the fixing carrier for the activated sludge, the firing temperatures of such ceramic articles are considerably high due to the increased cost cost of manufacturing, while conventional ceramic articles are not necessarily sufficient in fixing the activated sludge thereto. As described above, conventional carriers for fixing the activated sludge are not sufficient in affinity to the activated sludge, and therefore the reutilization properties, handling properties and are not adequate and cost high for treating huge amounts of the activated sludge. In the above, although the treatment of the sewage is described, the same problems as pointed out in the above description appear in the treatment of other waste water or industrial waste water, for example such as ammonia liquors discharged from coke ovens of the ironworks, waste water discharged from coal-gasification or liquefaction plants, waste water produced in the petroleum-refining process, waste water discharged from food-processing plants, waste water discharged from fermentation plants of alcohol and the like, and like waste waters.